2. Ken Carpenter, Chair of EUROCAE WG-75
Downlinking RAs to Controllers

3. Development of TCAS II
• TCAS II was developed as an airborne collision
avoidance system that is independent of
ground ATM systems, including controllers
– This was knowing and deliberate
• After considerable argument, in the face of
opposition, the ability to report RAs was
included.
– To enable ground monitoring of TCAS operation.

4. Pilot & Controller Interface
• PANS-OPS and PANS-ATM describe TCAS
procedures for pilots and controllers
• The pilot should follow TCAS RAs
– When he can, not “immediately”, he tells the
controller if he deviates from clearance
• The pilot obeys TCAS, not the controller
– “Negative, TCAS”
• When the pilot speaks thus,
the controller shuts up

5. Showing Controllers the RA
• RAs can be displayed to the controller
• The controller has a responsibility to
“separate” aircraft in an encounter
– He can say “avoiding action”
• But the controller sees the RA display,
and so says nothing
• The pilot chooses not to respond to the RA
– Perhaps relying on the controller
• The aircraft collide – Who is liable?